The present invention refers to a gluing machine and method for the gluing a final edge of a log.
Machines for gluing the edge of logs fed one after the other are currently known.
Such machines commonly successively comprise, following the direction of forward movement of the logs, an unwinding station for the logs to identify the final edge, a station in which the final edge is held, a station in which the log receives glue at an inner layer of paper with respect to that defined by the final edge, and a final rewinding station of the final edge onto the log in which, thanks to the glue transferred in the previous station, the edge is glued to the rest of the log.
An example of such a type of machine is described, for example, in patent EP541496. In EP541496 the forward movement of the log in the work station listed above is carried out by means of at least an upper belt that starts from the unwinding station of the logs and reaches at least the station in which the final edge is held if not, alternatively, the last rewinding station of the final edge onto the log.
In particular, in the prior art such an upper belt cooperates both with the forward movement of the log between the various stations as well as with some members of the stations themselves for the processing of the log while it rolls upon itself.
For example, the aforementioned upper belt cooperates at the bottom with inclined surfaces, as described in EP1609334, that can include belts or bands, as disclosed in EP541496 to make the logs move forward between the stations, but also with rollers or belts as mentioned in EP1440925 at the stations themselves.
Such known machines, although they do indeed allow the final edges to be glued on the relative logs, have some drawbacks linked to the speed of production of the finished logs that, due to what is described above, is closely linked to the forward movement speed of the aforementioned upper belt.
Such a limit derives from the fact that in known machines there are constructive elements that, cooperating both with the processing in some stations and with the forward movement of the logs between the work stations themselves, make the rolling speed of the log to be glued not able to be freely modified as desired from one station to the other.
In other words, in known machines the rolling speed of the log, with or without forward movement in a given station or in a section upstream or downstream of it, is unfortunately limited to a lower rolling speed required in another station in order to have a correct final gluing.
In particular, such a drawback is even more pronounced in the passage between the unwinding station in which the final edges of the logs are also identified, that is currently defined just by a lower roller and by the aforementioned upper belt, and the next station at which the log arrives again through the upper belt.
Indeed, it is known that in order to correctly identify the final edge, a step that has a direct influence upon the quality of the finished log, it is necessary to make the log rotate without feeding the log at a low speed. Conversely, once the final edge has been identified, it would be desirable to feed the log towards the next station as quickly as possible. However, since both the unwinding station and identification station of the final edge and the section for moving forward to the next station cooperate with the upper belt, the feeding speed of the log downstream of the unwinding is limited to the low rotation speed that allows correct identification of the final edge during the unwinding itself.
Consequently, in the section for feeding between the unwinding station and identification station of the final edge and the next station, the log, which could move forward at any speed without jeopardising the processing quality, moves forward at a very low speed limited by that of the upper belt that is indeed kept low to allow correct identification of the final edge during unwinding.